The present invention relates to the use of a laser for marking containers including container body ends and/or tab portions thereof and in particular to a process that can rapidly achieve the desired amount of marking within a predetermined time such as a manufacturing process dwell time.
As part of a container manufacturing, or in some cases, filling or sealing operation, markings may be placed on containers for a variety of purposes including identifying contents, identifying the location or date of manufacture or use, identifying the maker of the container or container component, the style or materials for the container, providing of trade names, advertising, promotion, or the like. In some situations, promotional information in the form of sweepstakes, contests, or other valuable tokens or indicia are placed or marked on container or container components.
A variety of devices and procedures have been used for marking containers. In some eases, embossing or incising processes have been used. Embossing or incising, e.g. via stamping, can require an undesirably large inventory of tools, e.g. for different kinds of lettering or symbols, and typically requires the need to shut down an assembly line and disassemble a press whenever it is desired to change tools (such as for changing the indicia being incised or embossed or for maintenance or repair purposes). Such shutdowns are particularly troublesome when it is desirable to change the symbols with relatively high frequency, such as when markings on containers are intended as part of a contest or sweepstakes in which there are preferably a relatively large number of different possible markings or indicia (e.g. when only some of which are xe2x80x9cgrand prizexe2x80x9d winners). Furthermore, it has been difficult to accurately control the depth of embossing or incising and, in some cases, embossing or incising that is too deep has led to leakage or container failure.
Accordingly, it would be advantageous to provide for marking of containers or components in a fashion permitting markings or indicia to be changed with relatively high frequency but without the need to stop or slow down a production line for this purpose. It would also be useful to provide for marking containers while avoiding the need for maintaining relatively large inventories of tools or dies, and preferably while avoiding container quality problems such as may arise from markings which are excessively deep.
Another process which has been used for placing markings on containers or components thereof, has been one or more printing processes. Contact or press printing is sometimes useful for decorating or placing markings on containers where it is desired to place a relatively large number of identical markings on containers. However, contact printing is believed impractical for many components, because of their shape or position (such as container-opening tabs) or when it is desired to change indicia with relatively high frequency (e.g. for sweepstake or contest purposes) because of the need to stop a production line and partially disassemble the contact print device in order to change the configuration of the items being printed on the containers.
In some situations, components of containers may be printed using a non-contact printing process such as an inkjet process. Although inkjets can be controlled to provide relatively frequent changes in indicia, inkjet processes and equipment have been found, in the past, to be relatively unreliable such as requiring frequent maintenance and repair. Inkjet processes have also been found to be subject to unwanted placement or positioning of ink such as resulting in a mist of ink which can interfere with the printing process, cause undesired markings on cans, or cause equipment malfunction. In some cases, it has been found that up to 20% or more of potential production time has been lost to the need for cleaning up, maintenance and/or repair when an ink jet process is used. Additionally, it has been found difficult to achieve reliable adhesion of the ink to containers or container components. Furthermore, when inkjet or other printing processes are used in connection with contest sweepstakes or providing other valuable tokens or indicia, since the process provides only surface markings (without forming indentations e.g. in the container itself) there is an undesirably large potential for counterfeiting or altering the markings e.g. in an attempt to claim a contest or sweepstakes prize. Furthermore, inkjet processes have been difficult to provide at high speed while maintaining quality, so as to mark letters or other indicia without distortion or the like.
Accordingly, it would be useful to provide for high quality marking of containers or container components while avoiding the cleanup, maintenance and repair time associated with inkjet or other printing processes, preferably while permitting relatively rapid changes of indicia.
Some or all of the above difficulties in previous container marking procedures are particularly troublesome for metallic containers or container components such as a typical aluminum alloy beverage container (e.g. of the type available from Ball Corporation, Broomfield, Colo.) or tabs or other components thereof. As compared with, e.g., plastic containers or container components, metal containers can be relatively difficult to mark, at least because it can be difficult to adhere ink to metal surfaces, because of the harder surface of metal containers, higher melting or softening point, and the like. Accordingly, devices and processes used in connection with some container materials are not necessarily applicable to others. In most situations, the functions or purposes for container markings will rarely justify use of procedures which would involve expenses which are substantially in excess of those involved with current processes. Accordingly, it would be useful to provide for procedures and devices for marking containers which can be achieved economically, preferably without substantially exceeding costs or expenses associated with current container production, filling or sealing processes.
The present invention provides for using laser light for marking metal containers or container components (including, e.g., container bodies, container ends and container end tabs). In one embodiment, a laser is provided with rapid-acting beam-steering and control to permit the marking of a relatively large number of characters or symbols (such as 6 or more, preferably 9 or more) in a relatively short period of time (such as less than about 100 milliseconds, preferably less than a normal component production dwell time e.g. of about 50 milliseconds) so that the desired marking can be achieved without stopping or slowing current container or container component fabrication procedures or machines.
In one embodiment, steering of a laser beam is achieved with high rapidity by reducing the mass of one or more steering mirrors. The resultant device delivers sufficient power density to form visible marks in a metal (e.g. aluminum) container component despite the decreased beam size or aperture associated with the smaller mirror size.
Preferably, the laser light is delivered to the container region or component as a series of high intensity laser pulses. Each pulse forms a visible ablated area or dot and the pattern of dots together make up the desired symbol or image. Accordingly, to achieve a desired number of characters or symbols in less than a predetermined period of time, the device must be capable of delivering all of the pulses needed for forming all of the desired characters within the predetermined time period. In one embodiment, a laser device is provided which delivers pulses at a frequency of at least about 12 kiloHertz (kHz) while providing sufficient power that substantially all such pulses produce the desired spot ablation of the metal container component. The use of a Nd:YVO4 laser has the advantage of improving the overall speed of the marking system since this type of laser uses a lasing medium (Vanadate) that can provide full power at higher frequencies without a diminishing of the power at higher frequencies as is inherent in Nd:YAG type lasers. The output power of an Nd:YAG laser begins to diminish above a frequency of 15 kHz as compared with 40 kHz and higher with a Nd:YVO4.
The laser marking of container ends with tabs can be done off-line. In another embodiment, such container ends that have been previously packaged and ready for attachment to can bodies are marked with indicia or additional indicia after being removed from their packaging. An off-line laser marking system is employed that is different from the conversion press used to form container ends with tabs. This off-line system can be used after container ends with tabs have already been formed and there is a need to add certain one or more marks.